1. Field of the Invention
This invention relates to a pulse generator which generates a clock pulse according to power-on or the reset of the power after an instantaneous power failure.
2. Description of the Related Art
A semiconductor integrated circuit is used various field. Recently, portable electronics device or equipments which has the integrated circuit are spreading.
The integrated circuit is able to action variously by being applied a predetermined voltage (e.g., a source voltage). The source voltage is applied the integrated circuit according to power-on to an apparatus having the integrated circuit.
The integrated circuit has an AND gate circuit, an OR gate circuit, or flip-flop circuit. The circuit such as the flip-flop circuit needs to set a initial state. The integrated circuit has a pulse generator to set the initial state.
The pulse generator generates a pulse signal for reset according to being up the source voltage applied the integrated circuit in the apparatus after power-on for the apparatus. Generally, the pulse signal is one-shot pulse signal. The circuit such as-the flip-flop circuit is set the initial state by receiving the pulse signal. The pulse generator is able to generate the pulse signal according to the reset of the power after an instantaneous power failure. As the pluse generator, these is known one disclosed in Japanese Patent Application Laid-Open Publication No. 2-138611, for example.
Generally, the source voltage applied to the integrated circuit is 5 V. But a recent integrated circuit uses a voltage which is deferent from 5 V by the source voltage (e.g., 3 V). When the pulse generator constructed assuming that the source voltage is 5V, is applied to the integrated circuit supplied with 3V as the source voltage, a pulse width of the pulse signal is longer than a pulse width of the pulse signal by using 5V by the source voltage. As a result, the pulse generator outputs the pulse signal a long time after the source voltage has completely risen. Therefore, the time required to bring the integrated circuit into an operating state, or the time required to bring the apparatus, which has the integrated circuit, into an operating state is long.
When the pulse generator constructed assuming that the source voltage is 3V, is applied to the integrated circuit supplied with 5V as the source voltage, a voltage level of the pulse signal changes from high voltage level to low voltage level before the source voltage has completely risen. As a result, the setting initial state for the circuit such as the flip-flop circuit uncomplete.
In the constructions disclosed the above-mentioned document, it seems that the pulse generator generates the pulse signal having the full-width for low source voltage by adjusting a time constant decided a resistance value of a resistive element and a capacitance value of capacitive element. But, in the constructions disclosed the above-mentioned document, it is not able to avoid to be long the time required to bring the integrated circuit into an operating state, or to increase in area of the pulse generator by widening a size the resistive element or the capacitive element.
It is an object of the present invention to provide a pulse generator for being able to reliably generate the pulse signal even when the circuit is applied to any source voltage.
It is another object of the present invention to provide a pulse generator for avoiding an increase in area.
It is further object of the present invention to provide a pulse generator for avoiding to be long the time required to bring the integrated circuit into an operating state into an operating state.